Solder composition substantially free of lead

ABSTRACT

This invention provides solder that is substantially free of lead that minimizes corrosion from occurring in the soldering equipment such as the tip of the soldering iron and soldering dipping tank. Without substantial, if any, amount of lead in the solder, the solder does not expose lead into the environment. The solder composition also includes element(s) that extend the life of the soldering tip or other equipments associated with soldering. The solder composition may include Sn (tin) along with Co (cobalt) and Fe (iron). Tin may make up the most of the content in the solder composition. The two elements cobalt and iron substantially inhibit tin from corroding the iron, thereby substantially preventing the soldering iron tip and dipping solder tank from corroding. The composition of the solder may also include Ag (silver) to improve the mechanical strength and wettability of the solder. Alternatively, the composition may include Ni (nickel) to improve the wettability of the solder as well, along with other elements.

1. RELATED APPLICATION

[0001] This application claims priority to a Japanese Patent Application no. 2003-013989 filed Jan. 22, 2003, entitled “Lead-Free Solder and Electronic Parts Using It,” which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 2. Field of the Invention

[0003] This invention relates to solder compositions for bonding electronic parts. In particular, this application relates to lead (Pb)-free solder composition that has tin (Sn) as the main element.

[0004] 3. General Background

[0005] In the electronic industry solders are used for connecting electrical leads and parts. A common solder contains tin (Sn) and lead (Pb) as its main elements with the lead content generally determining the eutectic temperature. For example, a lead base solder may contain 37% by mass. In recent years, a lead-free solder (or solder with small percentage by mass of lead equivalent to the contents of inevitable impurities) have been developed and used. The lead-free solders have been used because the lead in the solder contributed to acid rain, which in turn raises environmental concerns. Many lead-free solders have been proposed as discussed in the unexamined Japanese patent application No. H8-132277. When lead-free solder is used with a manual soldering iron, however, the useful life of the tip of the soldering iron is substantially shortened when compared to using solders with significant lead content.

[0006] One of the reasons for the shortened life of the tip is that the corrosion rate of the tip is increased with prior lead-free solder compositions. The soldering tip is usually made of copper or copper alloy, and its surface is plated with iron to prevent the solder from corroding the surface. The corrosion rate increases as the temperature of the soldering iron tip increases. The lead-free solder used for manual soldering generally has a higher melting point than the lead based solder. Accordingly, the operating temperature of the tip must be increased to solder with the lead-free solder as compared to the solder with lead content. With the increase in temperature of the tip, the iron plate on the tip corrodes faster thereby shortening the life of the tip.

[0007] Another reason for the shortened life of the tip is that the lead-free solder has more tin content than the lead solder. Tin is more reactive with the iron of the soldering iron tip further increasing the corrosion rate of the tip. In addition, the corrosion rate may be accelerated due to effects such as that of flux that is generally contained in solder used for manual soldering.

[0008] The corrosion problems have occurred in other soldering applications as well. For instance, in soldering applications where printed circuit boards with electronic components are immersed into melted lead-free solders, corrosion can occur to the walls of the solder tank, as well as the feed propeller and heating section. One of the reasons for the corrosion is that the solder tank is usually made of stainless steel, which has a large content of iron. The lead-free solders have larger amounts of particulates such as oxides, sludge, as well as tin, compared to the conventional lead-containing solder. The tin in the solder and iron in the stainless steel react to corrode the irons. In addition, the melting point of the lead-free solder is higher, which further accelerates the corrosion rate. These factors accelerate the corrosion rate of the dipping solder tank and shorten the useful life of the tank.

INVENTION SUMMARY

[0009] This invention provides a solder composition that is substantially free of lead to minimize exposing lead to the environment, and inhibit corrosion from occurring in the soldering equipment such as the tip of the soldering iron and solder dipping tank. The composition of the solder includes tin (Sn) along with cobalt (Co) and iron (Fe). Tin may make up the most of the content in the solder composition. The two elements cobalt and iron substantially inhibit tin from corroding the iron to substantially prevent the soldering iron tip and dipping solder tank from corroding. The composition of the solder may also include silver (Ag) to improve the mechanical strength and wettability of the solder. Alternatively, the composition may include nickel (Ni) to improve the wettability of the solder.

[0010] Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

[0012]FIG. 1(a) illustrates a front view of a testing apparatus for conducting the corrosion test.

[0013]FIG. 1(b) is a cross-sectional view of the leading end of a test specimen used for the corrosion test.

[0014]FIG. 2 is a graph illustrating the results of the corrosion test.

DETAILED DESCRIPTION

[0015] While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of this invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.

[0016] This invention provides a solder composition (also referred to as lead-free solder) that is substantially free of lead. The solder composition includes tin and silver, where tin makes up the largest percentage by mass of the solder composition. In addition, the solder composition may include either alone or in some combination such elements as iron, nickel, and cobalt. These elements may be incorporated into the solder composition to inhibit corrosion and improve the wettability. Besides these elements, other elements may be incorporated to the solder composition to inhibit corrosion from occurring in the soldering equipment, and to improve the strength and wettability of the solder.

[0017] The solder composition may include between about 0.01% and about 1.0% of iron by mass. With less than about 0.01% by mass of iron in the solder composition, there may not be enough iron in the composition to inhibit corrosion. On the other hand, with the content of iron in the solder composition in excess of about 1% by mass, the solder alloy may change to an oxidized state. In addition, the melting point of the solder composition may increase causing the soldering temperature to rise. Reducing the soldering temperature reduces the corrosion rate. Accordingly, the iron content in the solder composition may be between about 0.01% and about 1% by mass. In particular, the iron content in the solder composition may be between about 0.02% and about 1.0% by mass.

[0018] The content of cobalt in the soldering composition may be between about 0.01% and about 1.0% by mass. With less than about 0.01% by mass of cobalt in the solder composition, there may not be enough of cobalt in the composition to inhibit corrosion. On the other hand, with the content of cobalt in the solder composition in excess of 1% by mass, cobalt segregation may occur in the solder alloy. In addition, the melting point of the solder composition may increase causing the soldering temperature to rise. Accordingly, the cobalt content in the solder composition may be between about 0.01% and about 1% by mass. In particular, the cobalt content in the solder composition may be between about 0.02% and about 0.5% by mass.

[0019] The solder composition may also include nickel in the amount between about 0.01% and 1.0% by mass to minimize corrosion and improve the wettability. With less than 0.01% by mass of nickel in the solder composition, there may not be enough of nickel in the composition to inhibit corrosion. On the other hand, with the content of nickel in the solder composition in excess of 1% by mass, the solder alloy may change to an oxidized state. In addition, the melting point of the solder composition may increase causing the soldering temperature to rise. Accordingly, the nickel content in the solder composition may be between about 0.01% and about 1% by mass. In particular, the nickel content in the solder composition may be between about 0.02% and about 0.5% by mass.

[0020] Besides the individual content of iron, cobalt, and nickel, the total content of iron, cobalt, and nickel may also affect the melting point of the solder. That is, if the total content of iron, cobalt, and nickel exceed 1.0% by mass of the solder composition, then the melting point of the solder may rise and the corrosion rate may increase. Accordingly, the total content of iron, cobalt, and nickel may be less than about 1.0% by mass of the solder composition, and in particular less than about 0.7% by mass. The total content of iron, cobalt, and nickel, however, is not limited to being less than 1% by mass, and above percentage may be adjusted to minimize the corrosion effect on the solder composition.

[0021] The lead composition may include silver in the amount between about 0.2% and about 5.0%. With less than 0.2% by mass of silver in the soldering composition, there may not be silver content to improve the mechanical strength and wettability of the solder composition. On the other hand, incorporating more than about 5% by mass of silver may incur additional cost to formulating the solder. Accordingly, silver in the amount between about 0.2% and about 5.0% by mass of the solder composition may be used. In particular, silver content of between about 2.0% and 4.0% by mass may be used in the solder composition.

[0022] The solder composition may also include copper in the amount between about 0.1% and about 2.5% by mass. Incorporating copper into the solder composition may improve the wettability and decrease the melting point of the solder. Incorporating less than 0.1% of copper by mass may not be enough to improve the wettability and decrease the melting point. On the other hand, incorporating more than 2.5% by mass of copper into the solder composition may increase the viscosity of the solder in such a way that soldering defects may occur. Accordingly, the solder composition may include between about 0.1% and 2.5% by mass of copper. In particular, copper content in the solder composition may be about 0.2% and 1.0% by mass.

[0023] In addition to the above elements, the solder composition may include bismuth in the amount between about 0.1% and 5.0% by mass of the solder composition to improve the mechanical strength and decrease the melting point. Incorporating less than 0.1% of bismuth by mass into the solder composition may not improve the mechanical strength or decrease the melting point. On the other hand, incorporating more than about 5% by mass of bismuth into the solder composition may result in coarse solder alloy. Accordingly, the solder composition may include between about 0.1% and 5.0% by mass of bismuth, and in particular, between about 0.2% and 3.0% by mass.

[0024] The solder composition may include other elements such as zinc (Zn), stibium (Sb), indium (In), manganese (Mn), chromium (Cr), and palladium (Pd), to the extent that none of these elements adversely affect the iron, nickel, cobalt, silver, copper, and bismuth.

[0025] For manual soldering, the solder composition that is substantially lead-free may be shaped like a hollow wire containing flux as a core component. Electrical components such as a printed circuit board that has been soldered with lead free solder is beneficial to the environment because lead is not exposed to the environment. Also, with the solder composition described above, there is no trade off in terms of cost because the life of the iron tip and other equipment associated with soldering is approximately the same or longer as the life of the iron tip when soldering with lead based solder.

[0026] The lead composition may be formulated to shape like a solid wire or hollow wire having flux as its core component for use in manual soldering. In such application, the solder composition inhibits the iron-plated layer of the soldering iron tip from being corroded, thereby extending the life of the tip. In addition, other elements may be added to the solder composition to improve the wettability and the soldering efficiency.

[0027] The lead composition may be also formulated to be stored in the dipping solder tank for flow soldering application or used as solder paste for reflow soldering application. In this application, the solder composition inhibits the tank wall, feed propeller, and heating section of the dipping solder tank from being corroded, thereby extending the life of soldering equipment and increasing the wettability. That is, the solder composition may be used for soldering electrical components to a printed circuit board. In this application, even if the printed circuit board is discarded and later exposed to acid rain, minimal lead, if any, is released to the environment. In addition, the lead-free solder extends the life of the soldering iron tip and dipping solder tank and the replacement intervals, thereby increasing the productivity and reducing the cost of manufacturing the electronic parts.

[0028] The follow test results describe the corrosion test:

[0029] First Test:

[0030] FIGS. 1(a) and 1(b) illustrate a front view of the testing apparatus 1 for the corrosion test. The soldering iron 2 has a tip that is coupled to a test specimen 3. The Test specimen 3 is equivalent to a soldering iron tip. To measure the corrosion on the tip, test specimen 3 is shaped like a semi-cylindrical rod. The testing apparatus 1 allows the temperature of test specimen 3 to be maintained at a given value by controlling the heater that is provided in soldering iron 2. The testing apparatus 1 also includes a solder feeder 4 that is coupled to a solder specimen 5. The solder feed 4 is capable of moving axially as indicated by the arrow in FIG. 1(a). The test specimen 3 and the solder specimen 5 may be positioned so that they are axially aligned. As the solder feeder 4 moves the solder specimen 5 towards the test specimen 3, the leading end of solder specimen 5 makes contact with the test specimen 3. When the temperature of test specimen 3 is high enough, the leading end of solder specimen 5 melts and corrosion occurs in the test specimen 3. In this corrosion test, the solder specimen 5 was repeatedly melted and measured for the corrosion amount on the test specimen 3.

[0031]FIG. 1(b) is an enlarged view of the leading end of the test specimen 3. The test specimen 3 includes an iron-plated layer 12 (about 200 μm to about 300 μm) formed on the outer surface of copper-made test specimen base 10 shaped like a round rod. A thin Cr-plated layer 14 (about 2 μm to about 10 μm) is also formed on the iron-plated layer 12. The outer diameter of test specimen 3 is 5.4 mm. At the tip of the test specimen 3, an exposed area 13 is formed on the Cr-plated layer 14 with a diameter of 3 mm. This in turn exposes the iron-plated layer 12 in the exposed area 13. The solder specimen 5 is positioned so that it makes contact with the exposed iron-plated layer 12 around the exposed area 13. For the corrosion test, the corrosion amount on the iron-plated layer 12 in the iron-exposed area 13 is measured as indicated by the dotted line 18.

[0032] The solder specimen 5 used for the test had a diameter of 1.0 mm and contained flux. Approximately 3 percent of flux was impregnated at the center of the solder. Rosin-based or halogen-based type flux may be used. For this test, halogen-based flux was used.

[0033] Table 1 shows the test results of nine solder specimens that were evaluated. The test results excluded the flux components and the inevitable impurities. Column 1 lists the solder specimens indicated by numbers S1 through S6, and CS21 through CS23. The remaining columns indicate the test results, which are explained below in conjunction with FIG. 2. The numerical values in the table 1 represent percent by mass in relation to the composition. Test specimens S1 through S6 are solders where the large percentage by mass is tin, 3.5% of silver by mass, and remaining balance of iron-family of elements such as iron, nickel, and cobalt. For instance, specimen S1 is a solder containing 3.5% of silver and 0.02% of iron, with the rest being tin (hereafter referred to as Sn-3.5 Ag 0.02 Fe). Similarly, test specimen S2 hereinafter referred to as Sn-3.5 Ag-0.05 Fe; test specimen S3 hereinafter referred to as Sn-3.5 Ag-0.1 Ni; test specimen S4 hereafter referred to as Sn-3.5 Ag-0.1 Ni-0.05 Fe; test specimen 5 hereafter referred to as Sn-3.5 Ag-0.5 Co; and test specimen S6 hereafter referred to as Sn-3.5 Ag-1.0 Co.

[0034] Test specimens CS21 through CS23 are reference specimens used for the comparison purposes. Reference test piece CS21 is eutectic tin-lead solder that contains tin and 37% of lead by mass. Reference test pieces CS22 and CS23 are lead-free solder that have been used. CS22 is Sn-3.5 Ag, and CS23 is Sn-3.5 Ag-0.75 Cu. Specific Char- Sample acter No. No. Sn Pb Ag Cu Fe Ni Co S1 101 remainder 3.5 0.02 S2 102 remainder 3.5 0.05 S3 103 remainder 3.5 0.1 S4 104 remainder 3.5 0.05 0.1 S5 105 remainder 3.5 0.5 S6 106 remainder 3.5 1 CS21 (for 201 remainder 37 comparison) CS22 (for 202 remainder 3.5 comparison) CS23 (for 203 remainder 3.5 0.75 comparison)

[0035] Referring back to FIGS 1(a) and 1(b), for testing conditions, the temperature of the test specimen 3 was set at 300° C., 350-400° C. (at intervals of 10° C.), 425° C. and 450° C. The solder specimen 5 was fed 5 mm every 3 seconds towards the test specimen 3. This was done up to 5,000 times. When solder specimen 5 was fed 6 or 7 times to the test specimen 3, the melted solder dropped spontaneously.

[0036] After the solder specimen 5 was fed 5,000 times, the test specimen 3 was cut along the central line in a coaxial direction. The corrosion amounts of iron-plated layer 12 at the upper, central, and lower parts of iron-exposed area 13 were measured. The maximum was assumed as the measured value. FIG. 2 shows the results, where the horizontal axis shows the temperature (° C.) of the test specimen 3, and the vertical axis represents the corrosion amount (μm). The results of reference specimens CS21, CS22 and CS23 are shown as broken lines 201, 202 and 203, respectively.

[0037] The broken lines 202 and 203 corresponding to the specimens CS22 (Sn-3.5 Ag) and CS 23 (Sn-3.5 Ag-0.75 Cu), respectively, are conventional lead-free solder, which showed 3 to 5 times more corrosion occurring than the broken line 201 (Sn-37Pb) for the reference specimen CS21. In contrast, lines 105 and 106 corresponding to the test specimens S5 (Sn-3.5 Ag-0.5 Co) and S6 (Sn-3.5 Ag-1.0 Co), respectively, where cobalt was added, showed almost similar corrosion amounts as compared to the line 201. Accordingly, this test result demonstrates that the lead-free solder added with cobalt improves the resistance to corrosion.

[0038] Silver was added to the reference specimens CS21 through CS23 for mechanical strength of the solder composition, and therefore, excluded from the evaluation of the corrosion resistance. It was, however, noted that silver had an effect of improving the mechanical strength and wettability.

[0039] Lines 101 and 102 corresponding to the specimens S1 (Sn-3.5 Ag-0.02 Fe) and S2 (Sn-3.5 Ag-0.05 Fe), respectively, added with iron showed larger corrosion amounts than the line 201. However, these corrosion amounts were smaller than characteristics 202 and 203. Accordingly, adding iron to the lead-free solder improves the corrosion resistance.

[0040] Line 103 corresponding to the specimen S3 (Sn-3.5 Ag-0.1 Ni) added with nickel showed a larger corrosion amount than the lines 202 and 203. However, it was noted that adding nickel improved wettability. Line 104 corresponding to the test specimen S4 (Sn-3.5 Ag-0.1 Ni-0.05 Fe) added combination of nickel and iron. This combination improved corrosion resistance as compared to the line 103. In particular, at 400° C. or lower, the line 104 resulted in better corrosion resistance than the lines 202 and 203. In general, the operating temperature of the soldering iron tip, which is used for bonding electronic parts, is 350° C. to 400° C. When the solder is used for such an application, a practical effect of improving the corrosion resistance can be obtained. Cobalt may be used instead of iron to be combined with nickel. In this case, as illustrated by lines 105 and 106, a level equivalent to or better corrosion resistance as shown by line 104 may be expected. Accordingly, the addition of nickel plus iron or nickel plus cobalt to the solder composition improves the wettability, as well as the corrosion resistance within the range of operation temperatures such as below 400° C. The total content of iron, nickel, and cobalt in the solder composition may be between about 0.01% and 1.0% by mass, and in particular between about 0.01% and 0.7% by mass.

[0041] Second Test:

[0042] In the second test, a corrosion test was conducted as follows: the solder composition was melted and stored in the solder tank, a round iron bar (simulating the dipping solder tank) was dipped in the tank and the average corrosion amount was measured.

[0043] Table 2 shows the test results of four solder specimens that were evaluated in this test. The first column in table 2 lists the four specimens S11, S12, CS31, and CS32. S11 contains tin, 3.5% of silver, and 0.023% of iron by mass of the solder composition. S12 contains tin, 3.5% of silver, and 0.016% of iron by mass. CS31 and CS32 were also tested as references for comparison purposes. Reference piece CS31 is the eutectic tin-lead solder that contains tin and 37% of lead by mass. Reference piece CS32 is typical lead-free solder, which contains tin and 3.5% of silver by mass. Sample No. Sn Pb Ag Fe S11 remainder 3.5 0.023 S12 remainder 3.5 0.016 CS31 (for remainder 37 comparison) CS32 (for remainder 3.5 comparison)

[0044] For testing conditions, the temperature of the four solder specimens S11 and S12, and reference pieces CS31 and CS32 were set at 350° C., 400° C., and 450° C.; and the dipping duration of the round iron bar at 2, 4, 6, and 8 hours. Table 3 shows the test results. The first column indicates the data numbers (D1 through D7), the second column indicates the specimens, the third column indicates the dipping temperature (° C.), and the fourth column indicates the duration (h) in hours for test conditions, and the fifth column list the corrosion amount (μm) of the round iron bar after dipping. For example, Data 1 of table 3 shows that when the round iron bar of test piece S11 was dipped for 4 hours at 400° C., its corrosion amount was 2 μm. Data D1 through D7 similarly show the respective results. Temperature for Time for Erosion Saturation Saturation Amount Data No. Sample (submerge) ° C. (submerge) h μm D1 S11 400 4 2 D2 S12 350 6 3 D3 CS31 (for 450 2 8 D4 comparison) 450 8 60 D5 CS32 (for 450 2 30 D6 comparison) 400 4 25 D7 350 6 15

[0045] The comparison between the data D3 and D4 reveals that the corrosion amount increased as the reference piece CS31 was dipped for a longer time, e.g. from 8 hours to 60 hours. The comparison between the data D3 and D5 demonstrates that the corrosion amount of the conventional lead-free solder (tin and 3.5 % of silver by mass) was 3 times higher than that of the eutectic tin-lead solder. The comparison between the data D5 through D7 demonstrate that the dipping duration was increased from 2 to 4 and 6 hours, but the temperature was lower from 450° C. to 400° C. and 350° C., respectively. The result shows that corrosion amount decreased from 30 to 25 and 15 μm, respectively, indicating that the dipping temperature was influential with regard to corrosion on the specimen within the above dipping temperature and duration ranges.

[0046] The comparison between the data D1 and D6 demonstrates that for same testing conditions in terms of temperature and dipping duration (400° C. for 4 hours), the corrosion amount reduced from (2 μm) to (25 μm), respectively. Similarly, the comparison between the data D2 and D7 demonstrates that the corrosion amount reduced from (3 μm) to (15 μm), respectively, for the same testing conditions (350° C. for 6 hours). These comparisons indicate that the addition of iron to the solder composition that is substantially free lead decreased the corrosion amount.

[0047] The comparison between the data D1 and D2 indicates that between temperature range of 350° C. and 400° C., the corrosion amount of the lead-free solder added with iron was less affected.

[0048] The above test results indicate that adding iron to the solder composition inhibits melted solder from corroding the walls of the dipping solder tank and related equipment. As noted from the first test, cobalt may be used instead of iron, or the combination of iron and cobalt may be used to inhibit corrosion from occurring. Alternatively, the solder composition may be modified to minimize corrosion from occurring such as: (1) about 0.2% and 5% of copper by mass; or (2) about 0.1% and 5.0% of bismuth by mass.

[0049] The solder composition according to this invention is not limited to the elements or the percentage of mass for the elements used above for the purpose of the two tests. For example, the solder composition may be modified to incorporate copper between about 0.2% and about 5.0% by mass. The solder composition may also incorporate bismuth between about 0.1% and about 5% by mass.

[0050] In addition, other combination of elements not tested in table 1 may be incorporated into the soldering composition. For instance, the solder composition may include tin as its main element along with nickel, cobalt, and iron, where nickel and cobalt may each make up between 0.01% and 1.0% by mass with the total mass of iron, nickel, and cobalt being equal to or less than 1.0% by mass of the solder composition. Accordingly, alternative elements and different combination of elements may be incorporated into the solder composition to improve the mechanical strength and wettability of solder while inhibiting the tip of the soldering iron and the dipping solder tank from corroding. 

What is claimed is:
 1. A solder composition having substantial content of tin by mass, the solder composition further comprising: between about 0.2% and about 5% of silver by mass of the solder composition; and between about 0.01% and about 1.0% of iron by mass of the solder composition.
 2. The solder composition according to claim 1, further including: between about 0.1% and about 5.0% of bismuth by mass of the solder composition.
 3. The solder composition according to claim 1, further including: between about 0.1% and about 2.50% of cobalt by mass of the solder composition.
 4. The solder composition according to claim 1, further including: flux to formulate the solder composition into a wire.
 5. A solder composition having substantial content of tin by mass, the solder composition further comprising: between about 0.2% and about 5% of silver by mass of the solder composition; and between about 0.01% and about 1.0% of cobalt by mass of the solder composition.
 6. A solder composition having substantial content of tin by mass, the solder composition further comprising: between about 0.2% and about 5% of silver by mass of the solder composition; and between about 0.01% and about 1.0% of nickel by mass of the solder composition.
 7. A solder composition having substantial content of tin by mass, the solder composition further comprising: between about 0.2% and about 5% of silver by mass of the solder composition; between about 0.01% and about 1.0% of iron by mass of the solder composition; between about 0.01% and about 1.0% of cobalt by mass of the solder composition; and between about 0.01% and about 1.0% of nickel by mass of the solder composition, where the combined mass of the iron, cobalt, and nickel is less than about 1.0% of the solder composition.
 8. A solder composition having substantial content of tin by mass, the solder composition further comprising: between about 0.2% and about 5% of silver by mass of the solder composition; between about 0.01% and about 1.0% of nickel by mass of the solder composition; and between about 0.01% and about 1.0% of cobalt by mass of the solder composition, where the combined mass of the nickel and cobalt is less than about 1% of the solder composition.
 9. A process for soldering electrical components comprising: providing a lead-free solder including tin (Sn) as its main component and cobalt (Co), iron (Fe), and nickel (Ni) each in the amount of between about 0.01 to 1 percent by mass, and the combined amount of cobalt, iron and nickel being equal to or smaller than about 1 percent by mass; heating said lead free solder with a soldering iron to melt said lead free solder; and applying said melted lead free solder to an electrical component.
 10. The process of claim 9 wherein said lead free solder further comprises silver (Ag) in the amount of between about 0.2 to 5 percent by mass.
 11. The process of claim 9 wherein said lead free solder contains copper (Cu) in the amount of between about 0.1 to 2.5 percent by mass.
 12. A lead free solder composition for use in soldering electrical components wherein said lead free solder composition has a corrosive level approximately equal to lead based solder compositions, said lead free solder comprising:
 13. Tin (Sn) as its main component and cobalt (Co), iron (Fe), and nickel (Ni) each in the amount of between about 0.01 to 1 percent by mass, and the combined amount of cobalt, iron and nickel being equal to or smaller than about 1 percent by mass.
 14. The lead free solder of claim 12 further comprising silver (Ag) in the amount of between about 0.2 to 5 percent by mass.
 15. The lead free solder of claim 12 further comprising copper (Cu) in the amount of between about 0.1 to 2.5 percent by mass. 